APL and the VT FUZE The inexorable movement of the signals then interact to create a United States toward entry into "ripple" signal which is amplified World War II gave great urgency, in by vacuum tubes. When the pro­ 1940, to the search for new weapons jectile comes within a radius of about with which to combat a massive 70 feet from the target, the ripple enemy air threat. Among many such pattern becomes strong enough to weapons long envisioned was the trigger the thyratron tube that serves proximity fuze- a mechanism for as a switch. That action releases the detonating an explosive shell within electrical energy in a charged con­ kill range of an aircraft. While this denser, and the current, in turn, had long been considered impossible initiates an explosion in the electrical to attain, a project was nevertheless detonator, or squib. That blast launched in mid-August 1940, to activates the standard electrical investigate three possible mechanisms detonating fuze which sets off the for this type of fuze: photoelectric, main explosive charge in the pro­ acoustic, and radio. jectile. If the triggering pattern of the fuze coincided with the fragmentation Fuze Program Begins pattern of the shell, a "kill" was On June 27, 1940, the National probable .. In completed form, the Defense Research Committee had VT fuze consisted of four principal been founded, with Dr. Vannevar parts: A radio frequency oscillator and Bush as its chairman, to serve as a receiver, an amplifier and thyratron functioning link between the National tubes, a battery, and an explosive Academy of Science and the military train incorporating vital safety fea­ tures."l services. This organization, comprised of eminent scientists and educational Paralleling the scientific effort in leaders, was divided into divisions, of developing the so-called VT fuze, which Division A was to give its the organization supporting the work attention to problem,; of armor and was growing apace. Early work, with ordnance. Division A was further a handful of scientists, was done at the Carnegie Institution Department broken down into working teams, or Cutaway view of a typical VT fuze. sections, which would investigate of Terrestrial Magnetism. When the proximity fuze had emerged from the certain well-defined problems. One 1942, a production contract for a "impossible" category and was firmly of these had assigned to it the search basic model of the fuze, for Navy seated in the "probable," the need for for a proximity fuze; this was Section 5-in. guns, could be written. more space became desperate. In T, with Dr. Merle A. Tuve as its The VT (variable time), or consequence, all of Section T's work chairman (each section was known by proximity, fuze is clearly described by on projects other than the shell fuze its chairman's initial). At the time the Bureau of Ordnance: the con­ was removed physically and organiza­ of his appointment on Aug. 24, 1940, figuration selected as most promising tionally to the Bureau of Standards. Dr. Tuve was a member of the staff for anti-aircraft use was one "in of the Department of Terrestrial which the transmitter and receiver Founding of APL Magnetism of the Carnegie Institu­ were both located on the projectile. tion in Washington, D. C. This ... self-contained unit functions This move proved to be only temporary relief, however, with the From August 1940, until early in by transmitting a continuous pattern 1942, the radio shell fuze moved at a of [radio] waves in space. These ultimate result that on Mar. 10, 1942, fast pace through the phases of idea signals are reflected back to the a contract was signed by the Office of conception, search for components, oscillator by any target that gives a Scientific Research and Development testing, redesign, firing tests, and radio reflection. At first the pro­ and The Johns Hopkins University organizational growth in both jectile is so far from the enemy that which stipulated that the University numbers of personnel and the size of the signals are not returned with any would furnish laboratory space, facilities required. By Sept. 1941, after strength. As the projectile nears the equipment, test site, and additional frenzied effort, a complete fuze had target, however, the reflected waves 1 B. Rowland and W. B . Boyd, " U. S. Navy functioned properly at the end of its picked up by the oscillator grow Bureau of Ordnance in World War II," U. S. trajectory in a test firing. By Jan. stronger. The outgoing and incoming Government Printing Office, 1953, 278-279 . 18 APL Technical Digest personnel for furthering the VT fuze at the Silver Spring location. were tested under all conceivable program. Dr. Tuve was to continue The pressure for still more space operating conditions for all sizes of as head of the program, and overall continued, however. The rapidly guns for which radio fuzes were to be administration was transferred to the expanding program seemed always to produced, as well a3 for various OSRD. Dr. Tuve conceived the name be exasperatingly ahead of the avail­ changes in design intended to correct "Applied Physics Laboratory" for able physical facilities. In spite of a previous test failures. The search for the new organization operating under new building constructed just north of glass rugged enough to withstand the The Johns Hopkins University. the garage, plus two new floors added shock of gunfire was constant, as it With this brief background of the to the original building, and a new was for filaments, bridge wire, and emergence of the VT fuze, we may connecting building, the space avail­ wax. Even after the fuzes were in now look in some detail at the vastness able for the Laboratory's work never production, the test program ob­ of the fuze program and at its impact seemed to be adequate. jectives persisted in the quality control on the unfolding drama of World Needed facilities other than space program. War II*. to house the Laboratory included a Illustrative of the experience that The Johns Hopkins University new test field equipped with shelters supported the need for the continual entered upon its new responsibilities for the personnel conducting tests, program of testing, even through in a manner that gave promise of machine tools, instruments of various quantity production, is Dr. Tuve's continued rapid progress in the kinds, and other related equipment for summarization of the development of development of the VT fuze. The laboratory and field use. A suitable rugged tubes: President of the University appointed site at Newtown Neck, Md., was leased "Empirical factors enter in other ways D. Luke Hopkins, member of the and equipped for the safe conduct of than performance. For example, some Board of Trustees, as the official vertical recovery firings. design factors unpredictably limit representative of the University in all In spite of the many details that production. We started five companies matters pertaining to APL. Mr. had to be taken care of in the reloca­ on the design and manufacture of Hopkins stated that the University's tion to Silver Spring, and the establish­ rugged tubes, during 1940 to 1942. purpose was "to see to it that the job ment of new administrative and All designs were successfully rugged progressed as smoothly, expeditiously, communications channels, these tasks and made into successful fuzes. One and efficiently as possible." were accomplished in good time. The failed to make them on anything but The immediate task, of course, was increase in staff from 100 in 1942 to a laboratory basis, although large to provide whatever was most needed 700 in 1944, under difficult con­ amounts of money were spent on to enable Section T's expanding ditions imposed by the need for pilot production lines during two program to be carried on effectively complete secrecy, probably could years. The second has made rugged by the newly established Applied never have been done under the tubes continuously since early 1941. Physics Laboratory. The most im­ restrictions that had existed before Maximum production ever reached portant and most obvious requirement the entrance of The Johns Hopkins was 4000 per day, with limited use was additional personnel, but before University in the role of contractor­ of these tubes as substitutes. The third new staff could be taken on, office operator for the OSRD. company started 1940 with fairly and shop space adequate to ac­ successful tubes, kept in production commodate them had to be acquired. Problems of Design to early 1944, but could never exceed In Silver Spring, Md., a sparsely Recalling Dr. Tuve's statement 20,000 per day because the design settled cross-roads community at the that the success of this type of fuze was was not adapted to fast produc­ time, a garage was found which, it dependent on a great number of tion .... The fourth company is now appeared, would serve well for the empirical factors, each dependent our primary supplier (260,000 per present at least. upon design of specific components, day). The fifth company made two Lease of this property, 861 7 to we can appreciate the need for the million tubes, but characteristics 8621 Georgia Ave., was arranged by continuing program of testing. This were poor and fuzes variable. The the University to include not only the included complete fuzes as well as tubes were set aside and production garage floor but also the second and tubes, oscillator circuits, detonators, stopped early in 1943. (The sixth third floors which were then occupied explosive charges, and other com­ company was started and factory by a Social Security office. Many ponents. Among the latter were the built but the factory was turned over problems in adapting this building safety switches to prevent the shell to other work at our request.)"2 for use by the new Laboratory were from exploding either in the bore of a overcome in a short time in spite of gun or within 0.3 to 0.5 sec after Mass Production Begins wartime limitations on materials leaving the muzzle, and self-destruc­ As the first of the production fuzes and a tight labor market.